Inflatable stopping bags

ABSTRACT

A method of controlling the fluid pressure of an inflatable stopping bag used to block the fluid flow through a fluid conduit comprises pressurising the bag using a pressure regulator which operates to regulate the pressure of the bag as a function of the instantaneous pressure in the pipe upstream of the stopping bag.

[0001] This invention relates to inflatable stopping used to block thebore of a fluid conduit and provides a method and apparatus forregulating the pressure in such stopping bags when in use. Particularly,but not exclusively, the present invention provides a method andapparatus for regulating the pressure within stopping bags designed tobe inserted through a hole drilled in a liquid conduit, such as a watermains pipe, and then subsequently inflated to form a sealed blockage inthe pipe.

[0002] Inflatable stopping bags are widely used within the gas industryfor temporarily stopping the flow through a section of an in-service gasmains so that maintenance work can be performed on a section of the pipewithout removing the whole pipe from service. Typically two bags areused to seal the pipe upstream and downstream of the section to beworked upon. The bags are inserted in a deflated state throughrespective holes drilled in the pipe wall and then inflated into contactwith the inner wall of the pipe to block the pipe and isolate thesection to be worked. A bypass pipe is connected to respective holesdrilled upstream and downstream of the isolated section of the pipe toallow a gas flow to bypass the stopping bags and thus maintain service.

[0003] Although such stopping bag systems are widely used in the gasindustry they have to date had no significant use in the water industry.One reason for this is that the relatively high density and pressure ofwater within water mains (which can be at a pressure some ten timeshigher than that commonly found in gas mains) exerts much highermechanical forces on the stopping bag apparatus which can tend to pushthe bags along the pipe. Recently, however, a system has been developedby Glynwed Pipe Systems Ltd which provides a practical means ofmechanically supporting the bags in position to resist the forcesexerted by the relatively high pressure water. This is the subject ofPCT application number GB00/03771.

[0004] A further difficulty which is experienced when using stopping bagsystems in a water pipe is that the pressure in the pipe fluctuates inresponse to changing demand. Whereas in gas mains changes in demand havelittle effect on the pressure of the gas (which is compressible) thepressure can vary quite widely in a water main as demand changes due tothe incompressible nature of water. There is therefore a risk that ifthe water pressure rises significantly above the pressure in thestopping bag water may leak past the bag. There is also the potentialproblem that if the pressure in the water mains drops significantlybelow the pressure in the bag the bag may burst.

[0005] It is an object of the present invention to provide a way ofobviating or mitigating the potential problems mentioned above.

[0006] According to a first aspect of the present invention there isprovided a method of controlling the fluid pressure of an inflatablestopping bag used to block the fluid flow through a fluid conduit, themethod comprising pressurising the bag using a pressure regulator whichoperates to regulate the pressure of the bag as a function of theinstantaneous pressure in the pipe upstream of the stopping bag.

[0007] According to a second aspect of the present invention there isprovided apparatus for regulating the pressure in an inflatable stoppingbag for use in blocking a fluid conduit, the apparatus comprising apressure regulator which automatically regulates the pressure in thestopping bag when in use in response to the instantaneous pressurewithin the fluid conduit upstream of the stopping bag.

[0008] A specific embodiment of the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawing which is a schematic illustration of an embodiment of thepresent invention incorporated in a double bag stopping apparatusdesigned for blocking flow through a water mains pipe.

[0009] The invention is illustrated in use with a stopping bag systemaccording to Glynwed Pipe Systems Limited PCT Application NumberGB00/03771 mentioned above, which discloses one particular form ofstopping bag apparatus which is particularly suited for use in waterpipes.

[0010] The apparatus in accordance with the invention described below,can however be used with any conventional stopping bag system and thusdetails of the stopping bag insertion and support apparatus will be onlybriefly described.

[0011] Referring to the drawing, the illustrated stopping bag system isa double bag system comprising two identical stopping bags 1 a and 1 binstalled upstream and downstream of the working section 2 of a watermains pipe 3. In the drawing the bags 1 a and 1 b are shown in theirinflated state following insertion via respective bag insertionassemblies 4 a and 4 b which are themselves supported withinconventional machine housings 5 a and 5 b. The machine housings 4 a and4 b are each mounted to a machine base 6 a and 6 b which may be securedto the pipe 2 by a chain or the like (not shown) and sealed with respectof the pipe by an annular sealing member 7 a and 7 b. each machine base6 a, 6 b houses a sliding plate valve (not shown in detail) to allowaccess to the interior of the pipe through holes 8 a, 8 b. Each machinebase 6 a, 6 b thus provides a platform to which different machines canbe mounted to perform operations on the pipe 3. For instance, themachine bases 6 a and 6 b are initially used to support conventionaldrilling apparatus used to drill the holes 5 a, 5 b in the pipe 2through which the bags 1 a and 1 b are then inserted.

[0012] Each stopping bag apparatus comprises a support device 9 a,9 bmounted to the end of a respective post 10 a,10 b which is an extensionof a bag insertion tube 11 a, 11 b. The support devices 9 a,9 b supportthe inflated bags to resist the forces exerted on the bags in use by thewater pressure within the pipe 3.

[0013] Each of the machine assemblies 4 a and 4 b has a side pipe 12 a,12 b which are connected to a recharge pipe 13 and a vent pipe 14respectively by way of valved couplings 15 and 16. The recharge pipe 13provides a conduit for re-filling the working section of pipe 3 prior toremoval of the bags if necessary once the work is complete. The ventpipe 14 can be used to release air during the re-filling operation.

[0014] The recharge pipe 13 feeds from a bypass pipe 17 which isconnected between upstream and downstream bypass nipples 18 and 19 eachof which is provided with a respective valve 20 and 21 to control flowthrough the bypass pipe 17. The bypass pipe 17 is provided to allowwater to bypass the working section 2 of pipeline whilst work is beingcarried out and therefore maintain a water supply downstream of thestopping bag apparatus. In the illustration the bypass pipe 17 isrelatively narrow compared to the mains pipe 3 but may be much larger inpractice.

[0015] As mentioned at the beginning of this description, the details ofthe stopping bag apparatus itself, and the manner of its installation,may be entirely conventional and thus the particular apparatusillustrated has only been described above in brief outline. In use thebags 1 a, 1 b are inserted into the pipe 3 through the apertures 8 a, 8b in a deflated state by lowering the bag insertion tubes 11 a, 11 bthrough the machine assemblies 5 a, 5 b. The bag support devices 9 a, 9b are then deployed (in this instance the support devices 9 a, 9 bcomprise a plurality of slats which are fanned out across the bore ofthe pipe). The bags are then inflated by pumping a suitable fluid intothe bags 1 a, 1 b via inflation hoses 22 a, 22 b connected to respectiveinflation tubes 23 a, 23 b, via couplings 24 a, 24 b, which extendthrough the bag insertion tubes 11 a, 11 b.

[0016] The present invention provides a method and apparatus forsupplying pressurised fluid to the bags 1 a, 1 b (via the inflationhoses 22 a, 22 b) to both inflate and regulate the pressure within thebags 1 a, 1 b. Referring to the drawing, the illustrated embodiment ofthe invention comprises a pressure regulator 25 which provides means forboth inflating the bags 1 a and 1 b and for regulating the pressure inthe bags 1 a and 1 b as a direct function of the pressure within thepipe 3 upstream of the bag 1 a.

[0017] In more detail, the pressure regulator 25 comprises a cylinder 26within which is mounted a piston assembly 27. The cylinder 26 has arelatively large diameter chamber 26 a and a relatively small diameterchamber 26 b, an annular shoulder 28 being defined where the twoportions 26 a, 26 b meet (approximately mid way along the axis of thecylinder 26).

[0018] The piston assembly 27 comprises two connected pistons 27 a and27 b which are connected by way of rods 29. Each of the pistons 27 a and27 b comprises a disc which is sealed with respect to the internal wallof the cylinder 26 by piston rings 28 a and 28 b respectively. Thepiston 27 a has a larger diameter than piston 27 b and is in slidingengagement with the larger diameter cylinder chamber 26 a, smallerdiameter piston 27 b being in sliding engagement with the wall of thesmaller diameter cylinder chamber 26 b. The piston assembly 27 is freeto slide within the cylinder 26 so that the working volumes of thecylinder chambers 26 a and 26 b are variable. The pistons 27 a and 27 bare constrained to slide within the cylinder chambers 26 a and 26 brespectively by the relationship between the axial length of the rods 29and the axial length of the cylinder 26.

[0019] The pressure regulator 25 has an inlet pipe 30 extending from thecylinder 26 and opening into the bottom of the cylinder chamber 26 a.The inlet pipe 30 terminates in a valved coupling 31 and is providedwith a vent valve 32. An outlet 33 is provided in the cylinder head,i.e. at the top of the cylinder chamber 26 b.

[0020] Since in the illustrated embodiment the regulator 25 is used toinflate and pressurise two stopping bags 1 a, 1 b the outlet 33 isfitted with a Y piece 34 which is connected to bag inflation hoses 22 aand 22 b by way of valves 35 and 36 respectively. The cylinder head isalso provided with a removable plug 37 which may be removed to allow thecylinder chamber 26 b to be quickly filled or emptied of water. Apressure gauge 38 is provided to indicate the pressure within thecylinder chamber 26 b.

[0021] The drawing shows the apparatus in use with the bags 1 a and 1 balready inflated. However, the pressure regulator 25 has a duel functionin this embodiment, i.e. it is used to initially inflate the bags 1 a, 1b as well as to regulate the pressure within them. Operation of thepressure regulator 25 to both inflate the stopping bags 1 a and 1 b andregulate the pressure within them will now be described.

[0022] Prior to operation the cylinder chamber 26 b is filled with waterso that the piston assembly 27 lies at or near the bottom of its stroke.The inlet pipe 30 is then connected to an offshoot 39 of the bypass pipe17 with the valve 31 closed. The inflation hoses 22 a and 22 b areconnected to the Y piece 34, again with the valves 35 and 36 closed.Once the regulator 25 has been correctly connected the valves 31, 34 and35 are opened.

[0023] When the valve 31 is opened the pressure within the cylinderchamber 26 a rises to that of the water within the pipe 3 upstream ofthe bagging apparatus. This exerts a force on the piston 27 a which isgreater than that exerted on piston 27 b by the water pressure withincylinder chamber 26 b. The piston assembly 29 is driven upward by thepressure within the cylinder chamber 26 a thereby forcing water out ofthe cylinder chamber 26 b and into the bags 1 a, 1 b via inflation hoses22 a and 22 b, thereby inflating the bags. As the bags 1 a, 1 b areinflated the pressure within the bags, and thus within the cylinderchamber 26 b, increases. The piston assembly 27 will continue to forcewater into the bags 1 a, 1 b until the force exerted on the piston 27 bequals that exerted on piston 27 a, i.e. equilibrium is reached. Itwill, however, be appreciated that the force exerted on each piston is afunction of the pressure within the respective cylinder chamber 26 a, 26b and the surface area of the piston 27 a, 27 b. Thus, since the piston27 b has a smaller surface area than the piston 27 a, the pressure inchamber 26 b will be higher than the pressure in chamber 26 a when theequilibrium is reached. The pistons are relatively sized in this way toensure that the pressure within the bags 1 a and 1 b is slightly greaterthan that within the pipe 2 to provide an effective seal. Indeed, it hasbeen found that to provide an effective seal the bags should preferablybe pressurised to approximately 1.18 times the pressure within the pipe2 upstream of the bag. This is readily achieved by ensuring that thearea of the piston 27 a is 1.18 times as big as the area of piston 27 b.

[0024] Once the bag has been inflated, the pressure within the bags 1 aand 1 b is automatically regulated as a function of the pressureupstream of the pipe. That is, if the pressure in the pipe 3 drops thepressure in the chamber 26 a will drop so that the force exerted on thepiston 27 a will decrease allowing water to be forced back into thechamber 26 b from the bags until the force across the piston assembly 27has again been equalised. The reverse will of course occur should thepressure in the pipe 3 increase. It will be appreciated that as thepressure fluctuates in the pipe a corresponding fluctuation will occurin the pressure of the bags 1 a and 1 b which will always remain at apredetermined proportion of the pressure in the pipe 3 (eg 1.18 timesgreater than the pressure in the pipe).

[0025] Thus, the pressure regulator 25 operates both to inflate the bags1 a and 1 b and to ensure that the pressure within the bags is regulatedas a function of the pressure in the pipe 3 upstream of the baginstallation. Moreover, the particular pressure regulator illustratedachieves this without the requirement for any external power source,since the driving force is provided by the water pressure within thepipe 3. The gauge 38 provides a constant reading of the pressure withinchamber 26 a and thus the pressure within the bags 1 a and 1 b. It willalso be appreciated that because of the simple operation of theregulator 25 there is no delay between changes in the pressure withinthe pipe 3 and the bag 5.

[0026] Once the bags have been inflated, the downstream bypass valve 21could be opened (if it is not already open) to provide flow past theworking section of the pipe for as long as the work has been carriedout. At this time the recharge valve 15 will be closed. When the work iscomplete the recharge valve 15 is opened to refill the working sectionof the pipe 2. Once this has been refilled, the pressure unit controlvalve 3 is closed and the vent valve 32 provided in the inlet pipe 30 isopened. Water is then discharged via the vent valve 32 from the chamber26 a as water is forced back into chamber 26 b from the pressurised bags1 a and 1 b. In other words, opening the vent valve 32 allows the bagsto deflate re-establishing flow through the pipe section 2. Once thebags have been deflated the hose valves 35 and 36 may be closed and thehoses 22 a and 22 b disconnected from the bag insulation apparatus. Thebags and other machinery may then be removed and the holes 8 a, 8 b inthe pipe closed in accordance with conventional procedures.

[0027] The particular form of pressure regulator illustrated isadvantageously simple in construction and operation. It can be employedin the relatively hostile environments that may be found when working onpipe lines requiring no supervision and little maintenance. Aparticularly important advantage of the regulator illustrated is that itrequires no external power source as the driving force is provided bythe water within the pipe line 3. In addition, the regulator functionsboth to initially inflate the bags as well as to regulate the pressurewithin them once they are inflated. It will be appreciated, however,that many modifications could be made to the regulator.

[0028] For instance, the relative sizes of the pistons can be altered tomodify the ratio of the pressure within the pipe line 3 and within thebags 1 a and 1 b. Other details of the particular piston arrangement canof course vary widely. The function of this particular type of regulatorin which the water pressure in the bags is controlled directly as afunction as the pressure in the pipes just requires two pistonsmechanically linked together. For instance, the two pistons could movein quite separate chambers.

[0029] The regulator need not be used to initially inflate the bags aridsome other means could be provided to inflate the bags prior toconnection of the regulator. In addition, although water has been foundto be a particularly useful medium to inflate the bags other fluidscould be used. Liquids are however preferred due to their incompressible nature.

[0030] The regulator illustrated could be modified to take advantage ofthe water in the pipe 3 to fill the chamber 20 b prior to inflation ofthe bags. This could be achieved by the provision of valves whichinitially function to allow inlet water to fill the chamber 26 a butwhich automatically close when the chamber is full to allow thepressurisation of the bags to begin.

[0031] Whilst the illustrated embodiment of the invention isadvantageously simple, alternative embodiments might include pressureregulators driven by an external power source and which are providedwith compressors etc to regulate the pressure in the bags 1 and 2 inresponse to the pressure in the pipe 3. The essence of the invention isthe provision of a pressure regulator which automatically regulates thepressure within the bags in response to changes in the pressure withinthe pipe line 3. This could include microprocessor controlled systemswhich employ electronic transducers to monitor the pressure in thepipeline 3 and to control a pump/compressor and vent valves etc toregulate the pressure in bags 1 a and 1 b accordingly.

[0032] Whereas the invention is expected to be particularly useful inconjunction with stopping bags used in water pipes there is of course noreason why the invention cannot be used to regulate the pressure ofstopping bags used in other applications and is thus not limited tostopping systems designed for water pipes, or indeed liquid pipes.

[0033] Other possible modifications will be readily apparent to theappropriately skilled person.

1. A method of controlling the fluid pressure of an inflatable stoppingbag used to block the fluid flow through a fluid conduit, the methodcomprising: pressurising the bag using a pressure regulator whichoperates to regulate the pressure of the bag as a function of theinstantaneous pressure in the pipe upstream of the stopping bag.
 2. Amethod according to claim 1, wherein means are provided for transmittingthe pressure of the fluid in the pipe upstream of the stopping bag tothe pressure regulator, said transmitted pressure providing the forcerequired to pressurise the stopping bag.
 3. A method according to claim2, wherein the pressure regulator is connected directly between the pipeand the bag via a first fluid connection which is made between thepressure regulator and the pipe upstream of the stopping bag to transmitthe pressure of the pipeline to the pressure regulator, and a secondfluid connection from the pressure regulator to the stopping bag totransmit to the stopping bag, wherein the pressure maintained in thesecond fluid connection is regulated in direct response to changes ofpressure in the first fluid connection.
 4. A method according to claim3, wherein the pressure regulator comprises a first fluid chamber influid communication with said first fluid connection, a second fluidchamber in communication with said second fluid connection, a firstpiston moveable within said first fluid chamber in response to changesin pressure within the first chamber, and a second piston connected tosaid first piston which transmits the force exerted on the first pistonto the fluid within the second chamber and thus to the fluid within thesecond fluid connection and stopping bag.
 5. A method according to claim4, wherein the dimensions of the first and second chambers and first andsecond pistons are selected so that when the force exerted on the firstpiston by the fluid within the first chamber equals the force exerted onthe second piston by the fluid within the second chamber, the pressurein the second chamber is higher than the pressure within the firstchamber by a fixed predetermined proportion, such that the pressuremaintained within the stopping bag is always a fixed proportion of thepressure within the pipe upstream of the stopping bag.
 6. A methodaccording to any preceding claim, including the step of initiallyinflating the stopping bag using fluid supplied to the stopping bag fromthe pressure regulator.
 7. A method according to any preceding claim,wherein the fluid required for pressurising the stopping bag is suppliedto the pressure regulator from the pipe upstream of the stopping bag. 8.A method according to any preceding claim wherein the fluid conduit is awater pipeline.
 9. A method according to any preceding claim, whereinthe fluid used to pressurise the stopping bag is water.
 10. Apparatusfor regulating the pressure in an inflatable stopping bag for use inblocking a fluid conduit, the apparatus comprising a pressure regulatorwhich automatically regulates the pressure in the stopping bag when inuse in response to the instantaneous pressure within the fluid conduitupstream of the stopping bag.
 11. Apparatus according to claim 10,further comprising means for transmitting the pressure of the fluid inthe pipe upstream of the stopping bag to the pressure regulator, saidtransmitted pressure providing the force required to pressurise thestopping bag.
 12. Apparatus according to claim 10 or 11, wherein thepressure regulator operates to maintain the pressure in the stopping bagat a predetermined proportion of the instantaneous pressure of the fluidin the pipe upstream of the stopping bag.
 13. Apparatus according to anyone of claims 10 to 12, wherein the pressure regulator comprises a firstpiston moveable in a first piston chamber and a second piston moveablein a second piston chamber, the first chamber in use being pressurisedto the same pressure as the fluid upstream of the stopping bag, thesecond piston chamber in use being pressurised to the same pressure asthe fluid used to inflate the stopping bag, wherein the first and secondpistons are connected such that the force exerted on the first piston byfluid in the first piston chamber opposes the force exerted on thesecond piston by the fluid in the second piston chamber, so that thepistons tend to move to equalise the force exerted on each piston aspressure within the pipe varies, thereby regulating the pressure withinthe stopping bag in direct response to changes in pressure in the pipe.14. Apparatus according to claim 13, wherein the first and second pistonchambers are portions of a single cylinder, first and second pistonsbeing connected to reciprocate together along the axis of the cylinder.15. Apparatus according to anyone of claims 10 to 14, wherein therelative dimensions of the pistons and piston chambers are proportionedsuch that when the force exerted on each of the pistons is equalised thepressure within the second chamber is greater than the pressure withinthe first chamber so that the pressure in the stopping bag is alwaysgreater than the pressure in the pipe upstream of the stopping bag. 16.Apparatus according to anyone of claims 10 to 15, comprising a port forfilling said second chamber with fluid which fluid in use is used toinflate the stopping bag as the pistons move in response to fluidsupplied to the first chamber from the pipe upstream of the stoppingbag.
 17. Apparatus according to claim 16, wherein valve means areprovided for filling said second chamber with fluid from the pipeupstream of the stopping bag prior to pressurisation of the stoppingbag.
 18. A method of controlling the fluid pressure of an inflatablestopping bag used to block the fluid flow through a fluid conduit,substantially as hereinbefore described with reference to theaccompanying drawing.
 19. Apparatus for controlling the fluid pressureof an inflatable stopping bag used to block the fluid flow through afluid conduit, substantially as hereinbefore described with reference tothe accompanying drawing